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Fixing the Radiator Cooling Fan Problem on 02 MCS (with part numbers)
PO131 - Bank 2 O2 Sensor Low Voltage = due to fan running all the time, the first O2 sensor still thinks the car's engine is cold, making the 2nd O2 not run, thus not pulling power.
The car has been running rich (lesser MPG), due to the injectors pumping more fuel into the cylinders. This happens when the engine is cold upon start up, which is gauged by how much voltage is being pulled from the 2nd O2 sensor. Since the 2nd doesn't get hot enough, the car will run rich! Today I replaced the reservoir tank, put new coolant, and cleared the codes. I also completed the oil change with tune up, and the fan has stopped. Only thing is it is still not turning on the low speed, only high. Gas milage seems to have improved...
These are the parts that I have replaced:
Coolant Reservoir tank - 17137529273
Cooling Fan Relay -61366977982
Pending installation: Cooling Fan w/Resistor Assy - 17101475577 (pre 3/2003)
These are the services I have completed:
Coolant flush (done)
Oil Change + Tune Up (done)
I was told at one time the low speed dodad is actually within the fan motor housing. The high speed isn't. I can't say I ever saw a thread or printed information that concisely outlined where what is and what specific part failed. Nor whether anyone successfully fixed it simply by replacing a relay or resistor. I just know replacing the entire cooling fan assembly made mine all run properly.
Best of luck. Let us know what you learn in your endeavor.
